Domakihub Insulate Interior Walls with Rigid Foam Board in Greece
A practical retrofit guide for concrete-frame homes, holiday rentals, and hotels that cannot touch their facade.
Reviewed by Domakihub home & decor pros · 2026-06-23 · 5 min read
Greece's concrete-frame masonry buildings lose a surprising amount of winter heat through cold external walls — yet external cladding is often blocked by planning restrictions, tight urban plots, or shared building decisions. Interior rigid-foam insulation solves this without touching the facade, and the video above walks through the real-world method on an older property. This guide translates those principles into a step-by-step plan suited to Greek homes, holiday rentals, and small hotels looking to cut heating bills and improve guest comfort before the next cold season.
Why Interior Insulation Suits Greek Concrete-Frame Buildings
Most Greek residential and commercial buildings built between the 1960s and 1990s use a reinforced concrete skeleton with hollow brick infill panels. This construction is fast and affordable but thermally poor — the concrete columns act as cold bridges and the brick cavity offers only modest resistance. External insulation systems (ETICS) are the industry gold standard, but they require facade permits, unanimous co-owner agreement in apartment blocks, and scaffold budgets that deter most individual owners.
Interior rigid-foam board bypasses all of that. You work room by room, on your own timeline, without scaffolding or planning approval in most cases. The trade-off is a small loss of floor area — typically 8–10 cm per wall — and the need to temporarily remove skirting boards and reposition electrical outlets. For a holiday rental or hotel room that is already being refurbished, that disruption is barely noticeable alongside the payback in lower energy bills.
Choosing the Right Board for Greece's Climate
Two rigid-foam types dominate interior retrofit work: extruded polystyrene (XPS) and polyisocyanurate (PIR/PUR). XPS is widely available at Greek builders' merchants, resistant to the humidity found in island properties, and cost-effective at 60–80 mm thickness. PIR boards deliver higher thermal resistance per centimetre, making them the better pick where room depth is at a premium — a narrow Athenian apartment corridor or a Mykonos hotel suite, for example.
Avoid standard expanded polystyrene (EPS) on internal walls unless it carries a vapour-barrier facing; unprotected EPS can accumulate interstitial condensation inside Greek masonry walls that experience significant summer-to-winter temperature swings. Whichever board you choose, target a finished U-value of 0.35 W/m²K or below — that typically means 60 mm PIR or 80 mm XPS on a standard 20 cm brick-infill panel.
Five Steps to Install Rigid Foam Board on an Interior Wall
- 1
Prepare and dry the wall surface
Strip skirting boards, remove outlet covers, and inspect the wall for damp patches or rising moisture. In coastal Greek properties, salt efflorescence is common — brush it off and treat with a specialist salt-inhibiting primer. Any active leak or penetrating damp must be fixed before insulation goes in; trapping moisture behind foam board accelerates damage to the masonry. Allow at least two dry weeks after any remedial work before proceeding.
- 2
Mark and cut boards to size
Measure each wall section carefully, accounting for door reveals, window splays, and the positions of electrical back-boxes you will need to relocate. Score PIR or XPS board with a sharp utility knife and a straight edge — one firm pass on each face lets you snap a clean break. Cut boards 2–3 mm undersize on width so they slide into place without forcing; tight fits crack the foil facing on PIR and reduce the board's integrity at the joint.
- 3
Fix boards with adhesive and mechanical fasteners
Apply low-expansion PU foam adhesive or a compatible EPS/XPS adhesive in dabs around the perimeter and in a diagonal cross pattern across the board face — never a continuous bead, which traps air and causes uneven bond. Press each board firmly against the wall and hold for 60 seconds. Once the adhesive has cured overnight, add 4–6 plastic hammer-in anchors per board. On Greek brick-infill panels the anchors must hit the mortar bed or the concrete frame, not the hollow core of the brick, or pull-out strength will be negligible.
- 4
Tape joints and install a vapour control layer
Butt boards tightly and seal every joint with foil tape rated for thermal insulation. On walls facing north or that are in permanently humid spaces (bathrooms, basement holiday apartments), add a continuous vapour control layer (VCL) membrane over the foam surface before boarding over. In standard Greek living spaces with cross-ventilation, the foil facing on PIR already provides adequate vapour resistance — an additional membrane is optional but adds protection in island climates with high ambient humidity.
- 5
Board over, skim, and reinstate services
Fix 12.5 mm plasterboard over the foam using drywall screws long enough to pass through the board and anchor in the rigid foam substrate, or use a proprietary dot-and-dab system rated for insulated substrates. Tape and skim the plasterboard joints, reinstall skirting boards slightly thicker than the originals to cover the new reveal edge, and bring electrical back-boxes forward using proprietary spacer extensions — available at any Greek electrical wholesaler. Prime and paint as normal; the wall is ready to use within 48 hours of the final skim coat drying.
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FAQ
- Will interior foam insulation cause condensation problems in a Greek climate?
- Condensation risk is real but manageable. Greek winters are mild on the coast but cold inland, and the temperature differential across an insulated wall can push the dew point into the masonry. Sealing all board joints with foil tape and using PIR (which has a low vapour permeability facing) keeps moisture-laden interior air away from the cold wall behind. In high-humidity spaces such as island bathrooms or basement apartments, add an explicit vapour control layer and ensure the room has mechanical extract ventilation — a legal requirement under Greek building regulations for wet rooms in any case.
- How much floor area will I lose per room?
- A finished interior insulation system — 60 mm PIR board plus 12.5 mm plasterboard — projects 75–80 mm from the original wall face. On a standard 4 m wide room that means roughly 15 cm total loss in room width if both side walls are treated, equal to about 0.6 m² in a 4 x 4 m room. In practice, owners usually insulate the one or two coldest external walls rather than all four, keeping the footprint loss minimal. For holiday rental apartments where guest comfort and energy star ratings drive revenue, the trade-off is almost always worth it.
- Do I need a permit to insulate interior walls in a Greek apartment?
- Interior insulation that does not alter the building's external appearance, structural elements, or shared services generally does not require a building permit (oikodomiki adeia) under current Greek law. However, if you are in a listed building, a conservation zone, or an apartment block with shared ownership of partition walls, check with your local Urban Planning Office (Poleodomia) before starting. It is also courteous — and sometimes legally required — to notify the building's co-owners' committee (synidioktes) if works involve shared wall elements or temporary service interruptions.